The Autoregulatory Role of EsaR, a Quorum-Sensing Regulator in Pantoea Stewartii Ssp. Stewartii: Evidence for a Repressor Function

Mol Microbiol. 2002 Jun;44(6):1625-35. doi: 10.1046/j.1365-2958.2002.02987.x.

Abstract

Capsular polysaccharide synthesis and virulence in the plant pathogenic bacterium Pantoea stewartii ssp. stewartii requires the quorum-sensing regulatory proteins, EsaR and EsaI, and the diffusible inducer N-(3-oxo-hexanoyl)-L-homoserine lactone. Prior mutational studies suggested that EsaR might function as a repressor of quorum sensing in the control of capsular polysaccharide synthesis. Further, a lux box-like palindromic sequence coinciding with the putative -10 element of the esaR promoter suggested a possible negative autoregulatory role for EsaR. This report presents genetic evidence that EsaR represses the esaR gene under inducer-limiting conditions, and that addition of inducer promotes rapid, dose-dependent derepression. DNA mobility-shift assays and analyses by surface plasmon resonance refractometry show that EsaR binds target DNAs in a ligand-free state, and that inducer alters the binding characteristics of EsaR. Physical measurements indicate that the EsaR protein binds N-(3-oxo-hexanoyl)-L-homoserine lactone, in a 1:1 protein:ligand ratio, and that inducer binding enhances the thermal stability of the EsaR protein. These combined genetic and biochemical data establish that EsaR regulates its own expression by signal-independent repression and signal-dependent derepression. Additionally, we provide evidence that EsaR does not govern the expression of the linked esaI gene, thus EsaR has no role in controlling coinducer synthesis.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / biosynthesis
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / isolation & purification
  • Gene Expression Regulation, Bacterial*
  • Genes, Bacterial
  • Genes, Regulator / genetics
  • Homeostasis
  • Pantoea / genetics*
  • Promoter Regions, Genetic*
  • Transcription Factors / genetics*
  • Transcription Factors / isolation & purification

Substances

  • Bacterial Proteins
  • EsaI protein, Erwinia stewartii
  • EsaR protein, Pantoea stewartii
  • Transcription Factors